I would think water cooling is dependent upon the water cooling products moreso than the case. In addition, I believe the CM Cosmos is a complete overkill case and not worth the money. Isn't it like $300-400 while I'm sure the V2000 is in the $200 range and more plausible.

Oh, my bad. I could have sworn in some review I read it was priced nearly double that. Even so my aforementioned point still stands, the case shouldn't have too much bearing on how well the water cooling performs. It's all about the products you use and how efficient the connections are to the components. All cases deal with dissipating heat by air flow, it's just air cooled cases need it to be more specific or better due to it's reliability. Your components will stay very cool regardless of the internal case's ambient temperatures.